A computer network is a collection of interconnected computing devices that exchange data and share resources. In a packet-based network, such as the Internet, the computing devices communicate data by dividing the data into small blocks called packets, which are individually routed across the network from a source device to a destination device. The destination device extracts the data from the packets and assembles the data into its original form. Dividing the data into packets enables the source device to resend only those individual packets that may be lost during transmission.
Certain devices, referred to as routers, maintain routing information that describes routes through the network. A “route” can generally be defined as a path between two locations on the network. Upon receiving an incoming packet, the router examines information within the packet and forwards the packet in accordance with the routing information. To increase bandwidth available on the network, as well as the reliability and performance of the network, a destination router may be connected to a source router through multiple physical links, the physical links being terminated at respective egress ports of the source router. An operator may configure an aggregated interface within the source router to aggregate the multiple physical links as a virtual link referred to as an “aggregation group” or, alternatively, as a “link bundle.”
In order to maintain an accurate representation of the network, routers periodically exchange routing information in accordance with defined protocols. Large computer networks, such as the Internet, often include many routers grouped into administrative domains called “autonomous systems.” Routers within an autonomous system (AS) generally use interior gateway routing protocols (IGPs) for exchanging routing information internally. Examples of IGPs include Intermediate System to Intermediate System (IS-IS) and Open Shortest Path First (OSPF). Routers advertise links that are members of an aggregation group and connected to an aggregated interface as a single virtual link within IGPs to minimize the number of subnets distributed within an IGP domain.
The OSPF and IS-IS routing protocols are link state IGPs that use link state messages to ensure that the routing topology among routing protocol process instances of the AS routers are synchronized with respect to available interfaces, metrics and other variables associated with network links. OSPF uses Link State Advertisements (LSAs) while IS-IS uses Link State Protocol Data Units to exchange information. A router generating a link state message typically floods the link state message throughout the network such that every other router receives the link state message. In network topologies where routers are connected by point-to-point connections, each router floods link state messages to adjacent routers reachable on each interface to ensure synchronization. In networks using multi-access media, such as an Ethernet network, the routers within the network flood the link state messages to all other routers. In either case, the receiving routers construct and maintain their own network topologies using the link information received via the link state messages.